Dongqi Shi

Simple synthesis of yolk-shelled ZnCo2O4 microspheres towards enhancing the electrochemical performance of lithium-ion batteries in conjunction with a sodium carboxymethyl cellulose binder

Mixed metal oxides have been attracting more and more attention recently because of their advantages and superiorities, which can improve the electrochemical performance of single metal oxides. These advantages include structural stability, good electronic conductivity, and reversible capacity. In this work, uniform yolk-shelled ZnCo2O4 microspheres were synthesized by pyrolysis of ZnCo-glycolate microsphere precursors which were prepared via a simple refluxing route without any precipitant or surfactant. The formation process of the yolk-shelled microsphere structure during the thermal decomposition of ZnCo-glycolate is discussed, which is mainly based on the heterogeneous contraction caused by non-equilibrium heat treatment. The performances of the as-prepared ZnCo2O4 electrodes using sodium carboxylmethyl cellulose (CMC) and poly-vinylidene fluoride (PVDF) as binders are also compared. Constant current and rate charge–discharge testing results demonstrated that the ZnCo2O4 electrodes using CMC as the binder had better performance than those using PVDF as the binder. It was worth pointing out that the electrode using CMC as the binder nicely yields a discharge capacity of 331 mA h g−1 after 500 cycles at a current density of 1000 mA g−1, which is close to the theoretical value of graphite (371 mA h g−1). Furthermore, the obtained synthetic insights on the complex hollow structures will be of benefit to the design of other anode materials for lithium ion batteries.

PdNi hollow nanoparticles for improved electrocatalytic oxygen reduction in alkaline environments

Palladium-nickel (PdNi) hollow nanoparticles were synthesized via a modified galvanic replacement method using Ni nanoparticles as sacrificial templates in an aqueous medium. X-ray diffraction and transmission electron microscopy show that the as-synthesized nanoparticles are alloyed nanostructures and have hollow interiors with an average particle size of 30 nm and shell thickness of 5 nm. Compared with the commercially available Pt/C or Pd/C catalysts, the synthesized PdNi/C has superior electrocatalytic performance towards the oxygen reduction reaction, which makes it a promising electrocatalyst for alkaline anion exchange membrane fuel cells and alkali-based air-batteries. The electrocatalyst is finally examined in a H2/O2 alkaline anion exchange membrane fuel cell; the results show that such electrocatalysts could work in a real fuel cell application as a more efficient catalyst than state-of-the-art commercially available Pt/C.

Controlled Ag-driven superior rate-capability of Li4Ti5O12 anodes for lithium rechargeable batteries

AbstractThe morphology and electronic structure of a Li4Ti5O12 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5O12 nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional (1D) morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li4Ti5O12 nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li4Ti5O12 nanofibers, due to the Ag nanoparticles (<5 nm), which are mainly distributed at interfaces between Li4Ti5O12 primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li4Ti5O12 nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li4Ti5O12 anodes for lithium rechargeable batteries.

The effects of sintering temperature on superconductivity in MgB2/Fe wires

We studied the effects of sintering temperature on the phase transformation, lattice parameters, full width at half-maximum (FWHM), strain, critical temperature (Tc), critical current density (Jc) and resistivity (ρ) in MgB2/Fe wires. All samples were fabricated by the in situ powder-in-tube method (PIT) and sintered within a temperature range of 650–900 °C. It was observed that wires sintered at low temperature, 650 °C, resulted in higher Jc up to 12 T and lower Tc. The best transport Jc value reached 4200 A cm−2 at 4.2 K and 10 T. This is related to the grain boundary pinning due to small grain size. On the other hand, wires sintered at 900 °C had a lower Jc in combination with a higher Tc.

A phosphorus/N-doped carbon nanofiber composite as an anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) have been attracting intensive attention at present as the most promising alternative to lithium-ion batteries in large-scale electrical energy storage applications, due to the low-cost and natural abundance of sodium. Elemental phosphorus (P) is a very promising anode material for SIBs, with the highest theoretical capacity of 2596 mA h g−1. Recently, there have been many efforts devoted to phosphorus anode materials for SIBs. As pure red phosphorus cannot react with Na reversibly, many attempts to prepare composite materials containing phosphorus have been reported. Here, we report the facile preparation of a red phosphorus/N-doped carbon nanofiber composite (P/NCF) that can deliver a reversible capacity of 731 mA h g−1 in sodium-ion batteries (SIBs), with a capacity retention of 57.3% over 55 cycles. Our results suggest that it would be a promising anode candidate for SIBs with a high capacity and low cost.

Systematic study of a MgB2 + C4H6O5 superconductor prepared by the chemical solution route

We evaluated the additive effects of malic acid (C4H6O5), from 0 to 30 wt% of the total MgB2, on the lattice parameters, lattice strain, amount of carbon (C) substitution, microstructures, weight fraction of MgO, critical temperature (Tc), critical current density (Jc), and irreversibility field (Hirr) of a MgB2 superconductor. The calculated lattice parameters show a large decrease in the a-axis lattice parameter for MgB2+C4H6O5 samples from 3.0861(6) to 3.0736(1) A, with even a 10 wt% addition. This is an indication of C substitution into boron sites, with the C coming from C4H6O5, resulting in enhancement of Jc and Hirr. Specifically, the Hirr of the MgB2+C4H6O5 samples prepared by the chemical solution route reached around 7 T at 20 K, with a Tc reduction of only 1.5 K. In addition, the self-field Jc of the MgB2+C4H6O5 samples was only slightly reduced at an additive level as high as 30 wt%. However, residual oxygen after evaporation processing contributed to a large amount of MgO in our MgB2+30 wt% C4H6O5 samples. These problems can be further controlled by the amount of C4H6O5 additive or different evaporation temperatures.

N-doped crumpled graphene derived from vapor phase deposition of PPy on graphene aerogel as an efficient oxygen reduction reaction electrocatalyst.

Nitrogen-doped crumpled graphene (NCG) is successfully synthesized via vapor phase deposition of polypyrrole onto graphene aerogel followed by thermal treatment. The NCG was explored as an electrocatalyst for the oxygen reduction reaction, showing comparable electrocatalytic performance with the commercial Pt/C in alkaline membrane exchange fuel cells because of the well-regulated nitrogen doping and the robust micro-3D crumpled porous nanostructure.

Enhanced rate performance of cobalt oxide/nitrogen doped graphene composite for lithium ion batteries

Ultrafine Co3O4 nanocrystals homogeneously attached to nitrogen doped reduced graphene oxide (rGO) by the hydrothermal reaction method are demonstrated as anode materials for lithium ion batteries. Transmission electron microscope images revealed that the crystal size of Co3O4 in Co3O4/N-rGO and Co3O4/rGO is 5–10 nm, much smaller than that of bare Co3O4, indicating that the reduced graphene oxide sheets with Co3O4 nanocrystals attached could hinder the growth and aggregation of Co3O4 crystals during synthesis. The graphene sheets can also effectively buffer the volume change of Co3O4 upon lithium insertion/extraction, thus improving the cycling performance of the composite electrodes. The doped nitrogen on the reduced graphene oxide can not only improve the conductivity of the graphene sheets, but also introduce defects to store lithium and enhance the connection of the Co3O4 nanocrystals to the graphene sheet, leading to better distribution of Co3O4 on the graphene sheets, and enhanced rate performance. The nitrogen doping combined with the unique structural features is a promising strategy for the development of electrode materials for lithium ion batteries with high electrochemical performance.

TiO2 nanoparticles on nitrogen-doped graphene as anode material for lithium ion batteries

Anatase TiO2 nanoparticles in situ grown on nitrogen-doped, reduced graphene oxide (rGO) have been successfully synthesized as an anode material for the lithium ion battery. The nanosized TiO2 particles were homogeneously distributed on the reduced graphene oxide to inhibit the restacking of the neighbouring graphene sheets. The obtained TiO2/N-rGO composite exhibits improved cycling performance and rate capability, indicating the important role of reduced graphene oxide, which not only facilitates the formation of uniformly distributed TiO2 nanocrystals, but also increases the electrical conductivity of the composite material. The introduction of nitrogen on the reduced graphene oxide has been proved to increase the conductivity of the reduced graphene oxide and leads to more defects. A disordered structure is thus formed to accommodate more lithium ions, thereby further improving the electrochemical performance.

Binder‐Free and Carbon‐Free 3D Porous Air Electrode for Li‐O2 Batteries with High Efficiency, High Capacity, and Long Life

Pt-Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon-free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O2 and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt-Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm(-2) . Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high-efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research.